Long-term instability of the East Archimedes slope failure headscarp: a case history

Authors: Easby, B; Mullenbach, J; Becker, R; George, T Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2535_21

Cite As:
Easby, B, Mullenbach, J, Becker, R & George, T 2025, 'Long-term instability of the East Archimedes slope failure headscarp: a case history', in JJ Potter & J Wesseloo (eds), SSIM 2025: Fourth International Slope Stability in Mining Conference, Australian Centre for Geomechanics, Perth, https://doi.org/10.36487/ACG_repo/2535_21



Abstract:
In late 2013, the south highwall of the East Archimedes open pit at the Ruby Hill mine collapsed after many months of detailed monitoring and analysis, leaving behind a near-vertical 90 m high headscarp. The south highwall consists of cemented alluvium that performed very well in previous phases of mining at slope angles steeper than 55°. The mechanism of failure was postulated to be due to deformation of the underlying intrusive rock in response to stress relaxation of the rock mass during mining, and shear strain localisation at the base of the alluvium resulting in a weakening of the materials at or near the contact between the alluvium and underlying rock. Since the initial slope failure, the headscarp remained near-vertical with relatively little additional deformation, with the exception of some surficial spalling and ravelling from the headscarp face. In 2021, additional mining was completed in the bottom of the pit, opposite the slope failure and headscarp. In the winter of 2022, nearly 9 years after the 2013 failure and approximately 3 months after mining in the bottom of the pit was completed, a substantial portion of the headscarp failed. Following, additional smaller failures of the headscarp in the same region occurred. This paper aims to review the mechanism of failure in the 2013 and 2022 events to better understand the relationship between mining in the pit and the stability of the headscarp.

Keywords: cemented, alluvium, instability, case history, Nevada

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